TOXICOLOGY

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TOXICOLOGY

• ENVIRONMENTAL RESEARCH

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Why study Toxic Risk?

• Make decisions about the safety of your food.
• Help you make informed public policy decisions.
• Be able to separate real risks from imaginary
  ones.
• Learn some basic research techniques.

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Questions for your own Research.

• What does Toxic mean?
• What is Safe food and water?
• How can you improve or change an experiment to
  answer new questions?

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More on your Research

• Do your answers lead to new questions?
• You should
• Discuss your ideas with classmates.
• Exchange feed back.
• Make constructive criticisms.
• Collaborate on joint projects.

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The Dose Makes the Poison.

• Definition Toxicity How poisonous a substance
  is to organisms.
• All substances are poison there is none which
  is not a poison. The right dose differentiates a
  poison from a remedy.
• Philippus Paracelsus (early 1500s)

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Any Chemical Can Be Toxic

• Which is more poisonous caffeine or
  trichloroethylene (dry cleaning fluid)?
• Caffeine 50 times normal daily dose can be
  fatal
• Vitamins A and D can also kill you in high enough
  doses.
• To learn about trichloroethylene go to
  www.sciLINKS.org type in codeATR02

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Are Natural Chemicals Safer?

• That depends.
• Lots of organisms make toxins for defense or to
  help get food.
• Lots of synthetic chemicals are safe.
• Anything can be a poisonous in high enough doses.

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How much is too much?

• A chemicals short-term toxicity is measured with
  a dose/response study.
• Definitions
• Dose The total amount of a chemical that an
  individual eats, breathes, or absorbs through the
  skin.
• Exposure - Coming in contact with a chemical
  through food, water, air, or other sources.

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• Response- changes in organisms caused by
  exposure to a toxin.
• Usually the higher the exposure the greater the
  response.
• Dose/Response experiments are called bioassays.
• Assay means test.

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Dose/Response Bioassays

• Bioassays use organisms to measure a chemicals
  toxicity.
• Example
• Lab rats each get just one dose of a chemical
• Doses range from very low to very high.
• At the end of 14 days any deaths or other health
  responses are recorded.

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Dose/Response Bioassays

• There should also be a control group.
• In a well designed experiment, some but not all
  rats should survive.
• You then get a number called LD50
• The LD50 is the Lethal dose for 50 of the
  treated organisms.
• i.e. Half the rats that got the LD50 dose were
  dead after 14 days.
• LD50 is in milligrams of the chemical per
  kilogram of body weight (mg/kg).

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Dose/Response Bioassays

• Remember usually some individuals will die at
  lower doses and some will be able to take very
  high doses with little or no harm.
• For bioassays
• www.sciLINKS.org Code ATR02

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A Typical Dose/Response Curve
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Comparing Chemical Toxicities

• 14 day bioassay does not consider long term
  effects.
• LD50 doses can vary a lot from one species to
  another.
• WHY?
• Animals vary in metabolism.
• Differences in absorption, storage and excretion
  of chemicals.

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Comparing Chemical Toxicities

• Animal Experiments
• Go to www.sciLINKS.org Code ATR03
• Sometimes toxicology studies are now done on
  single cells or blood samples.
• These have limits

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Lethal Doses of some Common Compounds
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Toxicity Categories Used for Human Poisons
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Long-Term vs. Short-Term Toxicity

• Definitions
• Acute effects are caused by exposure to a single
  dose.
• Chronic effects develop slowly due to long term
  exposure.

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Long-Term vs. Short-Term Toxicity

• LD50 bioassays concern only acute effects.
• Our body can get rid of many chemicals so long
  term exposure is no problem.
• Other chemicals can build up slowly even with low
  doses and cause health problems.

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Long-Term vs. Short-Term Toxicity

• Some things can cause one kind of acute problem
  with one time, high doses.
• Other problems with long-term chronic lower
  doses.
• Example

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Testing Chronic Toxicity

• Feed lab animals relatively low doses each day
  for long periods of time.
• Look for negative effects not death rates
  (examples)
• Lower growth rates
• Behavior changes
• Lower immunity to disease
• Reproduction problems
• Shorter life span

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Why?

• Acute and Chronic Bioassays are the basis for
  gov. regulations about food, water, drugs,
  cosmetics, etc.